1. Field of the Invention
The present invention relates to a system and method for controlling simultaneous arrival of two or more calls and more particularly, to a system and method which enables separate connection control in response to simultaneous arrival of a plurality of calls in a switching system having a plurality of terminal control equipment units connected to a network termination unit and an arbitrary number of separate terminals connected with each terminal control equipment unit.
2. Description of the Related Art
In a known system developed for use in an integrated services digital network (ISDN), a network termination unit is connected with a digital exchange through digital subscriber lines and a plurality of terminal control equipment units. The terminal control equipment units can in turn be connected to telephone sets, facsimile devices, data terminals, telex terminals, and so on.
Various combinations of channels have been proposed. For example, there is a system using several B channels of 64 Kb/s as communication channels and a D channel of 16 Kb/s as a channel for a control signals and slow packets thus combining a plurality of B channels with a D channel.
Since two or more B channels are established for communication between an exchange and the terminal control equipment units, both a first incoming call and a second incoming call may be received at the same time. With the arrival of the first incoming call, however, the terminal control equipment units enter into an alerting state. When the second incoming call arrives, the terminal control equipment units send release signals because of the "busy" state for the second incoming call.
As described above, when two or more incoming calls arrive simultaneously, the exchange receives a ringing signal when a first incoming call is received. It therefore processes other incoming calls as in a "busy" state even if some B channels are free. Thus, when two or more incoming calls arrive, connect processing is possible only for the first incoming call. This is disadvantageous from the viewpoints of serviceability as well as the efficient utilization of the system.